An inkjet printer is a fluid ejection device that provides drop-on-demand ejection of fluid droplets through printhead nozzles to print images onto a print medium, such as a sheet of paper. Inkjet nozzles can become clogged and cease to operate correctly, and nozzles that do not properly eject ink when expected can create visible print defects. Such print defects are commonly referred to as missing nozzle print defects.
In multi-pass printmodes missing nozzle print defects have been addressed by passing an inkjet printhead over a section of a page multiple times, providing the opportunity for several nozzles to jet ink onto the same portion of a page to minimize the effect of one or more missing nozzles. Another manner of addressing such defects is speculative nozzle servicing in which the printer ejects ink into a service station to exercise nozzles and ensure future functionality, regardless of whether the nozzle would have produced a print defect. In single-pass printmodes, missing nozzle print defects have been addressed through the use of redundant nozzles on the printhead that can mark the same area of the page as the missing nozzle, or by servicing the missing nozzle to restore full functionality. However, the success of these solutions, particularly in the single-pass printmodes, relies on a timely identification of the missing nozzles.